package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.index.FieldInfo.IndexOptions;
import org.apache.lucene.index.FreqProxTermsWriterPerField.FreqProxPostingsArray;

// TODO FI: some of this is "generic" to TermsHash* so we
// should factor it out so other consumers don't have to
// duplicate this code

/** Used by DocumentsWriter to merge the postings from
 *  multiple ThreadStates when creating a segment */
final class FreqProxFieldMergeState {

    final FreqProxTermsWriterPerField field;
    final int numPostings;
    final CharBlockPool charPool;
    final int[] termIDs;
    final FreqProxPostingsArray postings;
    int currentTermID;

    char[] text;
    int textOffset;

    private int postingUpto = -1;

    final ByteSliceReader freq = new ByteSliceReader();
    final ByteSliceReader prox = new ByteSliceReader();

    int docID;
    int termFreq;

    public FreqProxFieldMergeState(FreqProxTermsWriterPerField field) {
        this.field = field;
        this.charPool = field.perThread.termsHashPerThread.charPool;
        this.numPostings = field.termsHashPerField.numPostings;
        this.termIDs = field.termsHashPerField.sortPostings();
        this.postings = (FreqProxPostingsArray) field.termsHashPerField.postingsArray;
    }

    boolean nextTerm() throws IOException {
        postingUpto++;
        if (postingUpto == numPostings)
            return false;

        currentTermID = termIDs[postingUpto];
        docID = 0;

        final int textStart = postings.textStarts[currentTermID];
        text = charPool.buffers[textStart >> DocumentsWriter.CHAR_BLOCK_SHIFT];
        textOffset = textStart & DocumentsWriter.CHAR_BLOCK_MASK;

        field.termsHashPerField.initReader(freq, currentTermID, 0);
        if (field.fieldInfo.indexOptions == IndexOptions.DOCS_AND_FREQS_AND_POSITIONS)
            field.termsHashPerField.initReader(prox, currentTermID, 1);

        // Should always be true
        boolean result = nextDoc();
        assert result;

        return true;
    }

    public String termText() {
        int upto = textOffset;
        while (text[upto] != 0xffff) {
            upto++;
        }
        return new String(text, textOffset, upto - textOffset);
    }

    public boolean nextDoc() throws IOException {
        if (freq.eof()) {
            if (postings.lastDocCodes[currentTermID] != -1) {
                // Return last doc
                docID = postings.lastDocIDs[currentTermID];
                if (field.indexOptions != IndexOptions.DOCS_ONLY)
                    termFreq = postings.docFreqs[currentTermID];
                postings.lastDocCodes[currentTermID] = -1;
                return true;
            } else
                // EOF
                return false;
        }

        final int code = freq.readVInt();
        if (field.indexOptions == IndexOptions.DOCS_ONLY)
            docID += code;
        else {
            docID += code >>> 1;
            if ((code & 1) != 0)
                termFreq = 1;
            else
                termFreq = freq.readVInt();
        }

        assert docID != postings.lastDocIDs[currentTermID];

        return true;
    }
}
